linux-kernel - Re: [PATCH] Repalce strncmp by memcmp

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Date:	Tue, 30 Nov 2010 11:27:51 +0100
From:	Bernd Petrovitsch <bernd@...rovitsch.priv.at>
To:	Ryan Mallon <ryan@...ewatersys.com>
Cc:	Steven Rostedt <rostedt@...dmis.org>, pavel@...linux.ru,
	LKML <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH] Repalce strncmp by memcmp

On Die, 2010-11-30 at 11:51 +1300, Ryan Mallon wrote:
[...] 
> It can still break things in subtle ways. Lots of the replacements are
> of the form:
> 
>   if (strncmp(string, "foo", 3) == 0)
> 
> Which can only be replaced with memcmp if the minimum length of string
> is _always_ 3. This may be true for some callsites (with careful audit),
> but in general I doubt it is and it will lead to subtle bugs.
> 
> I hardly think it is worth auditing a bunch of strncmp calls to ensure
> that the minimum length of the checked string is always n in order to
> remove a single instruction. Making such a change will also introduce
> subtle bugs if the rules for the string ever change, eg. a change is
> made to allow string = "".

On the conceptual level:
And it will confuse people if strings (read: '\0' terminated char arrays
specified by a pointer to the start) with raw memory (read: memory with
arbitrary content - including '\0' not at the end - specified by a
pointer to the start and the valid size).
Even more confusing is that raw memory *may* hold a string ...

Don't get me wrong: every seasoned C programmer should know that. But
not everyone is one ...

Bernd
-- 
Bernd Petrovitsch                  Email : bernd@...rovitsch.priv.at
                     LUGA : http://www.luga.at

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